The governing Liberals have reversed their 2011 decision to close the jail to save money following an "internal evaluation of operational needs."
They decided to keep the jail open due to growing need for space in Ontario's correctional system and after hearing community concerns, the government said Monday.
"Our staff is already dealing with capacity pressures throughout the provincial correctional system," Community Safety and Correctional Services Minister Madeleine Meilleur said in a release.
"We are taking action to deal with those pressures. Keeping the Sarnia Jail open makes sense and will provide additional beds and much-needed space, creating a safer environment for our employees."
Nearly half of Ontario's jails are overcrowded, a six-year high that sees cells meant for two people at times holding three or more as the province struggles with a rising tide of inmates who have yet to have their day in court.
Statistics by the Ministry of Community Safety and Corrections show that on an average day last year 14 of the province's 29 jails held more prisoners than they were designed for.
The province closed a jail in Owen Sound and another in Walkerton in 2011. At the time, the Liberals said all three closures would save about $8 million a year by moving the inmates to newer and larger facilities in Windsor and Penetanguishene, north of Barrie.
But critics insisted it would spark court delays, send transportation costs soaring and devastate rural communities.
Rather than save money, a community group said closing the Sarnia jail would actually end up costing provincial and municipal taxpayers $3 million a year.
Save the Sarnia Jail committee said the facility was still needed because municipal and provincial police, as well as First Nations police, the Canada Border Services Agency and the RCMP all use it, it said.
Closing it could also create legal problems if inmates moved to Windsor had difficulty consulting with their lawyers in Sarnia, and it could prevent offenders from serving their sentences on the weekend, it said.
The facility also has a tunnel that connects it to the courthouse, which means the costs associated with transporting inmates to their court appearances is minimal.
NDP critic Taras Natyshak said it took too long for the Liberals to see the light.
"It's unfortunate that it took two years of backlash for Meilleur to finally listen to Sarnia," he said in a statement.
"We need a corrections system that is safe, effective and efficient."
(The Canadian Press, BlackburnNews.com)